Disks such as magnetic and optical disks which are information recording media or substrate disks therefor have a hole in the center, through which spindles pass to permit the rotational driving of the disks. Such disks are tested by an inspector to see whether they have any surface defects or if they have sufficient electrical performance to be useful as recording media. The testing process usually comprises providing a cassette containing a plurality of disks, picking up each disk from the cassette by holding it with a disk chucking mechanism and loading it on the inspector. The loaded disk is mounted on a given spindle on the inspector and driven to rotate for testing. After the end of testing, the disk is unloaded from the inspector and either replaced in the same cassette or placed in a different cassette.
FIG. 4 shows an exemplary cassette containing magnetic disks (which are hereunder referred to simply as "disks") and FIG. 5 shows an exemplary disk chucking mechanism which picks up each disk from the cassette. As shown in FIG. 4, individual disks 1 are contained in a box or cassette 2 with an open top such that the periphery of each disk is exposed from the top. Being positioned that way, the disk is chucked at two sites, one being at 1a on the peripheral edge of the exposed part and the other being at 1b on the peripheral edge of the top of the center hole. The thus chucked disk 1 is picked up from the open top of the cassette 2.
The disk chucking mechanism is shown specifically in FIGS. 5(a) and 5(b). FIG. 5a is a schematic side view showing its interior. The disk chucking mechanism (hereunder referred to simply as a "chucking mechanism") 3 comprises a pressure roller 31a having a V-shaped groove and which is to be urged against the peripheral edge 1a of the exposed part of the disk, a pressure roller 31b also having a V-shaped groove and which is to be urged against the peripheral edge 1b of the top of the center hole, as well as air cylinders 32a and 32b for driving these rollers, respectively. The chucking mechanism 3 is mounted on a hand RH provided at the distal end of a handling robot.
The chucking mechanism 3 first drives the air cylinders 32a and 32b such that their piston rods are extended to increase the distance between the two pressure rollers 31a and 31b, as shown by dashed lines in FIG. 5a. The hand RH then pushes the chucking mechanism 3 to have the roller 31b positioned in such a way that the V-shaped groove corresponds to the periphery of the center hole in the disk whereas the roller 31a is positioned in such a way that the V-shaped groove corresponds to the periphery of the exposed part of the disk. Subsequently, the chucking mechanism 3 drives the air cylinders 32a and 32b in directions opposite to the previous ones so that their piston rods contract to reduce the distance between the rollers 31a and 31b, whereupon the disk 1 is chucked with the peripheral edges 1b and 1a being depressed by the V-shaped grooves of the rollers 31b and 31a, respectively.
In another type of the chucking mechanism 3, each of the air cylinders 32a and 32b may be loaded with a coil spring such that the rollers are moved by the urging force of the coil springs during the chucking or unchucking operation. In this case, air may be introduced into the respective cylinders at the time of either chucking or unchucking the disk. For the sake of simplicity, FIGS. 5(a) and 5(b) show the case of chucking the peripheral edge 1a with one roller 31a but, in the usual case, two rollers 31a are spaced apart to depress the peripheral edge 1a of the exposed part of the disk by bringing them closer to the roller 31b in a manner relative to each other. This is in order to ensure that the disk can be chucked with a specified pressure being applied to both the periphery of the center hole in the disk and the periphery of the exposed part of the disk.
Recent versions of disks are available in various sizes in decreasing order of 5.25 inches, 3.5 inches, 3.3 inches, 2.5 inches, 2.0 inches and 1.8 inches. On the other hand, the conventional chucking mechanism 3 is limited in the distance between rollers 31a and 31b and different units of the chucking mechanism are employed for different sizes. Hence, several units of the chucking mechanism 3 are provided to handle the various disk sizes and replacement is made as it becomes necessary. However, the replacement step is by no means efficient since it requires not only manpower but also time. Under the circumstances, it has been desired to develop a chucking mechanism that requires neither replacement operations nor manpower but which can handle various sizes of disk in one unit.
A problem with the conventional chucking mechanism having the aforementioned structure is that if the distance between rollers 31a and 31b is initially set at a large value and then reduced by moving either one of the rollers or both, the roller stroke required to chuck the disk becomes different from one roller to another. This introduces difficulty in chucking the disk with the depressing pressure on its outer and inner peripheral edges being maintained within a predetermined fixed range. If the distance between the rollers is set to comply with larger disks, errors are prone to occur when chucking smaller disks; on the other hand, if the distance between the rollers is set to comply with smaller disks, the required roller-to-roller distance cannot be ensured for larger disks.